Nearly twenty percent of adolescents have health consequences attributable to persistent medical, behavioral, or other health conditions, and the number of adolescents with special health care needs (ASHCN) that survive into adulthood continues to increase. There is evidence that patient-centered medical home (PCMH) health care delivery model provides children more effective, efficient, and timely care at lower cost, particularly among the highest utilizers: children with special health care needs. What we do not know is how PCMH may benefit ASHCN as they grow into adulthood. It is also not known how the health care system best serves ASHCN whose conditions differ in severity and duration. The investment in PCMH is high and therefore, we need to learn whether it improves utilization of preventive care over more expensive hospital-based services, whether pediatric PCMH providers are helping ASHCN transition to adult providers, and how utilization and transition depend on medical complexity. The long-term goal of our research is to improve the quality of primary care for ASHCN. The overall objective of this R03 proposal is to quantify the impact of pediatric PCMH on ASHCN health care utilization and transition to adult care capitalizing on our ability to link Vermont's all-payer medical claims database with practice-level details of PCMH recognition from the National Center for Quality Assurance (NCQA). The rationale for the proposed research is that understating the impact of PCMH on ASHCN by medical complexity will allow for the development or modification of practice-based quality improvement approaches to support the health and transition goals of ASHCN, tailored to ASHCN medical complexity. The hypotheses are that ASHCN in PCMH will have more primary care visits, fewer emergency room visits, fewer inpatient stays, fewer hospital readmissions within 30 days, and will be more likely to successfully transition to adult providers than ASHCN not in PCMH. The two studies proposed to test these hypotheses are designed to (1) measure the impact of PCMH recognition on health care service utilization among ASHCN by level of medical complexity and (2) assess the successful transition of ASHCN from a pediatric PCMH to an adult provider by ASHCN level of medical complexity. The approach is innovative because it will move the current state of ASHCN research past self-report measures and highlight the emerging importance of medical complexity in questions about health care resource use. The proposed research is significant because it will test the impact of PCMH on the goals of ASHCN to transition to adult providers and to receive primary care for prevention and wellness. Understanding this impact will inform future efforts to spread the PCMH model to support the health of ASHCN and inform efforts to take a patient-oriented approach to this support by considering medical complexity.